Product image resource in REST now returns a media image GID to streamline migration to GraphQL

As of 2025-01, the admin REST API for the product image resource will return a media image GID instead of a product image GID. This is designed to help make it easier to migrate to GraphQL from REST when interfacing with product images that were created before the introduction of a unified media id.

Previously, the admin_graphql_api_id returned a product image ID: "gid://shopify/ProductImage/43701248884792"

Now, the admin_graphql_api_id will return a media image ID: "gid://shopify/MediaImage/12379812379123"

This change will only affect clients using the latest 2025-01 API version. Older versions will continue to return the ProductImage GID, ensuring backward compatibility. It's strongly recommended to upgrade to using GraphQL as REST is nearing deprecation.